1. Field of the Invention
The present invention relates to an organic light-emitting diode (OLED) device. More particularly, the invention relates to a flexible organic electroluminescent device having an increased lifespan by preventing introduction of water thereto, and a method for fabricating the same.
2. Discussion of the Related Art
An organic light-emitting diode (OLED) device, one type of flat panel display device, has high brightness and a low operation voltage. Further, the OLED device has a high contrast ratio because it is a spontaneous light-emitting type, and it can implement a display of an ultra thin thickness. The OLED device can easily implement moving images due to a short response time corresponding to several micro seconds (μs). The OLED device has no limitation in a viewing angle, and has a stable characteristic even at low temperatures. Further, as the OLED device is driven at a low voltage such as a direct current of 5-15 v, it is easy to fabricate and design driving circuits.
The OLED device can be fabricated in a very simple manner because only deposition and encapsulation equipment is required.
The OLED device having such characteristics is largely categorized into a passive matrix type and an active matrix type. In the passive matrix type, scan lines and signal lines cross each other to form an OLED device in a matrix form. In order to drive each pixel, the scan lines are sequentially driven. Accordingly, for a required average brightness, an instantaneous brightness, a value obtained by multiplying an average brightness by the number of lines, should be implemented.
On the other hand, in the active matrix type, a thin film transistor (TFT), a switching device for turning on/off a pixel region, is located at each pixel region. A driving thin film transistor connected to the switching thin film transistor is connected to a power line and a light-emitting diode, and is formed at each pixel region.
A first electrode connected to the driving thin film transistor is turned on/off in unit of a pixel region, and a second electrode facing the first electrode serves as a common electrode. The first electrode, the second electrode, and an organic light-emitting layer interposed between the two electrodes constitute the light-emitting diode.
In such an active matrix type, a voltage applied to a pixel region is charged in a storage capacitor (Cst). Power should be applied to the OLED device until a subsequent frame signal is applied to the OLED device. Under such configuration, the OLED device is continuously driven for a single frame, regardless of the number of scan lines.
Even if a low current is applied to the OLED device, the same brightness is implemented. Owing to characteristics of low power consumption, high resolution and a large screen, the active matrix type is being spotlighted in recent years.
A basic structure and an operation characteristic of such an active matrix type OLED device will be explained with reference to the attached drawings.
FIG. 1 is a circuit diagram illustrating a configuration of a single pixel region of an active matrix type OLED device in accordance with the related art.
Referring to FIG. 1, a single pixel region of an active matrix type OLED device is composed of a switching thin film transistor (STr), a driving thin film transistor (DTr), a storage capacitor (Cst) and a light-emitting diode (E).
Gate lines (GL) are formed in a first direction, and data lines (DL) are formed in a second direction perpendicular to the first direction, thereby defining pixel regions (P). A power line (PL) for applying a power voltage to the OLED device is spaced from the data line (DL).
A switching thin film transistor (STr) is formed at an intersection between the data line (DL) and the gate line (GL), and a driving thin film transistor (DTr) electrically connected to the switching thin film transistor (STr) is formed in each pixel region (P).
The DTr is electrically connected to a light-emitting diode (E). More specifically, a first electrode, a terminal disposed at one side of the light-emitting diode (E) is connected to a drain electrode of the DTr. A second electrode, a terminal disposed at another side of the light-emitting diode (E) is connected to a power line (PL). The power line (PL) transmits a power voltage to the light-emitting diode (E). A storage capacitor (Cst) is formed between a gate electrode and a source electrode of the DTr.
When a signal is applied to the OLED device through the gate lines (GL), the STr is turned on. The DTr is turned on as a signal of the data lines (DL) is transmitted to the gate electrode thereof. Accordingly, light is emitted through the light-emitting diode (E). If the DTr is turned on, a level of a current applied to the light-emitting diode (E) from the power line (PL) is determined. As a result, the light-emitting diode (E) can implement a gray scale. The storage capacitor (Cst) serves to maintain a gate voltage of the DTr constantly when the STr is turned off. Accordingly, even if the STr is turned off, a level of a current applied to the light-emitting diode (E) can be constantly maintained for the next frame.
FIG. 2 is a sectional view illustrating an OLED device in accordance with the related art.
FIG. 3 is a sectional view taken along line “III-III” in FIG. 2, which schematically illustrates an OLED device in accordance with the related art.
FIG. 4 is an enlarged sectional view of part ‘A’ in FIG. 3, which illustrates that water introduced into an OLED device through side surfaces of the OLED device spreads through a bank and a planarization layer.
Referring to FIG. 2, in the related art OLED device, an active area (AA, display region) and a non-active area (NA, non-display region) formed outside the active area (AA) are defined on a substrate 11. A plurality of pixel regions (P) defined by gate lines (not shown) and data lines (not shown) are formed at the active area (AA). A power line (not shown) is formed in parallel to the data lines (not shown).
A switching thin film transistor (not shown) and a driving thin film transistor (DTr) are formed at each pixel region (P).
In the related art organic light-emitting diode device, the substrate 11, where the DTr and the light-emitting diode (E) have been formed, is encapsulated by a barrier film (not shown).
The related art OLED device will be explained in more detail. As shown in FIG. 3, an active area (AA) and a non-active area (NA) formed outside the active area (AA) are defined on a substrate 11. A plurality of pixel regions (P) defined by gate lines (not shown) and data lines (not shown) are formed at the active area (AA). A power line (not shown) is formed in parallel to the data lines (not shown).
A buffer layer (not shown), formed of an insulating material, e.g., an inorganic insulating material such as silicon dioxide (SiO2) or silicon nitride (SiNx), is formed on the substrate 11.
A semiconductor layer 13 is formed at each pixel region (P) in the active area (AA) above the buffer layer (not shown). The semiconductor layer 13 is formed to correspond to a driving region (not shown) and a switching region (not shown). The semiconductor layer 13 is composed of a first region 13a formed of pure poly silicone and forming a channel; and second regions 13b and 13c formed of pure poly silicone, disposed at two sides of the first region 13a, and to which impurities of high concentration are doped.
A gate insulating layer 15 is formed on the buffer layer (not shown) including the semiconductor layer 13. A gate electrode 17 is formed on the gate insulating layer 15 in correspondence to the first region 13a of the semiconductor layer 13 in the driving region (not shown) and the switching region (not shown).
A gate line (not shown), connected to the gate electrode 17 formed at the switching region (not shown) and extending to one direction, is formed on the gate insulating layer 15.
An interlayer insulating layer 19 is formed on an entire surface of the substrate including the gate electrode 17 and the gate line (not shown), in the active area. Semiconductor layer contact holes (not shown), through which the second regions 13b and 13c disposed at two sides of the first region 13a of the semiconductor layer 13 are exposed to outside, are provided at the interlayer insulating layer 19 and the gate insulating layer 15 formed therebelow.
Data lines (not shown), which define the pixel regions (P) by crossing the gate lines (not shown) and formed of a second metallic material layer, are formed on the interlayer insulting layer 19 including the semiconductor layer contact holes (not shown). A power line (not shown) is formed in a spaced manner from the data lines. The power line (not shown) may be formed on the gate insulating layer 15 where the gate lines (not shown) have been formed, in a spaced manner from the gate lines (not shown), in parallel thereto.
A source electrode 23a and a drain electrode 23b, made of the same second metallic material as the data lines (not shown), are formed at a driving region (not shown) and a switching region (not shown) on the interlayer insulating layer 19. The source electrode 23a and the drain electrode 23b are spaced from each other, and contact the second regions 13b and 13c exposed to outside through the semiconductor layer contact holes (not shown). Under such configuration, the semiconductor layer 13, the gate insulating layer 15, the gate electrode 17 and the interlayer insulating layer 19 sequentially deposited on the driving region (not shown), form a driving thin film transistor (not shown), together with the source electrode 23a and the drain electrode 23b which are spaced from each other.
A planarization layer 25, having a drain contact hole (not shown) through which the drain electrode 23b of the driving thin film transistor (DTr) is exposed to outside, is formed on the driving thin film transistor (DTr) and the switching thin film transistor (not shown).
A first electrode 31, which contacts the drain electrode 23b of the driving thin film transistor (DTr) through the drain contact hole (not shown), is formed on the planarization layer 25 in a separated manner for each pixel region (P).
A bank 33 is formed on the first electrode 31, in the non-active area (NA), i.e., an area outside each pixel region (P). The bank 33 is formed so that the pixel regions (P) can be separated from each other.
An organic light-emitting layer 35, composed of organic light-emitting patterns (not shown) which emit red, green and blue light, is formed on the first electrode 31 in each pixel (P) enclosed by the bank 33.
A second electrode 37 is formed in the active area (AA) of the substrate including the organic light-emitting layer 35 and the bank 33. The first electrode 31, the second electrode 37, and the organic light-emitting layer 35 interposed between the two electrodes 31 and 37 form a light-emitting diode (E).
For prevention of introduction of water into the OLED device, a passivation layer 39 is further formed on the entire surface of the substrate 11 including the second electrode 37.
A barrier film 43 is positioned on the entire surface of the substrate 11 including the passivation layer 39 in a facing manner, for encapsulation of the light-emitting diode (E). An adhesive 41 is interposed between the substrate 11 and the barrier film 43, so that the substrate 11 and the barrier film 43 can be completely attached to each other without an air layer therebetween. The passivation layer 39, the adhesive 41 and the barrier film 43 have a face seal structure.
As the substrate 11 and the barrier film 43 are attached to each other by the adhesive 41 to thus form a panel, the OLED device 10 according to the related art is complete.
However, the related art OLED device may have the following problems:
Firstly, in the related art face seal structure, e. g., in a lamination structure among the passivation layer 39, the adhesive 41 and the barrier film 43, the passivation layer 39 and the barrier film 43 serve as a barrier for preventing introduction of water into the OLED device. However, the adhesive 41 cannot serve well as a barrier. This means that introduction of water occurs easily from the side surfaces of the OLED device, rather than from the upper surface.
Secondly, if foreign materials or cracks do not occur between thin films in the related art face seal structure, introduction of water into the OLED device does not occur. However, as shown in FIG. 4, introduction of water into the OLED device actually occurs due to foreign materials, etc. generated when a lower layer is processed.
Especially, step coverage of the passivation layer 39 forms a boundary around foreign materials. In this case, the boundary serves as a passage through which water is introduced into the OLED device.
Water introduced into the adhesive 41 having a low barrier function is firstly introduced into the OLED device, through the boundary. Then, the water is secondary introduced into the OLED device, through a lower organic layer of a thin film transistor, e.g., a bank and a planarization layer. This may result in oxidation of a cathode of the OLED device.